Parviz Moin

Bio: Parviz Moin is an academic researcher from Stanford University. The author has contributed to research in topics: Turbulence & Large eddy simulation. The author has an hindex of 116, co-authored 473 publications receiving 60521 citations. Previous affiliations of Parviz Moin include Center for Turbulence Research & Ames Research Center.

Large-eddy simulation of a rotor tip-clearance flow

Abstract: A large-eddy simulation (LES) solver which combines an immersed-boundary technique with a curvilinear structured grid has been developed to study the temporal and spatial dynamics of a rotor tip-clearance flow, with the objective of determining the underlying mechanisms for low pressure fluctuations downstream of the rotor near the endwall. Salient feature of the numerical methodology, including the mesh topology, the treatment of numerical instability for non-dissipative schemes in a highly skewed mesh, and the parallelization of the code for shared memory platforms are discussed. Qualitative agreements have been observed between present LES and experimental measurements. The simulations indicate that the interaction between the moving endwall boundary layer and blade boundary layers and tip-leakage flow creates a highly complicated flow which is dominated by distinct vortical structures including the tip-leakage and tip-separation vortices. These vortical structures are found to convect downstream, expand in size and generate intense turbulent fluctuations in the endwall region.

Feedback algorithms for turbulence control - Some recent developments

Abstract: Some recent developments on the feedback control of turbulent ows are presented. Physical mechanisms associated with opposition control algorithms are investigated. A new control method based on the sensing and manipulation of vorticity creation at the wall is presented. The results indicate that signiicant drag reduction can be achieved using wall information only. The potential for optimization of feedback control algorithms, using neu-rocomputing methodologies is outlined.

Wall-Modeled Large-Eddy Simulation of Turbulent Boundary Layers with Mean-Flow Three-Dimensionality

Abstract: We examine the performance of wall-modeled large-eddy simulation (WMLES) to predict turbulent boundary layers (TBLs) with mean-flow three-dimensionality. The analysis is performed for an ordinary-d...

A New Paradigm for Simulation of Turbulent Combustion in Realistic Gas Turbine Combustors Using LES

Abstract: This paper presents a new paradigm for numerical simulation of turbulent combustion in realistic gas turbine combustors Advanced CFD methods using Large Eddy Simulation (LES) turbulence models are central to this paradigm in fluid dynamics where engineers can apply the full predictive abilities of numerical simulations to the design of realistic gas turbine combustors The use of LES models is motivated by their demonstrated superiority over RANS to predict turbulent mixing The subgrid scale models incorporated in LES are based on the dynamic approach where the model coefficients are computed rather than prescribed by the user This has provided unparalleled robustness to modern turbulent flow computations using LES A new numerical algorithm was derived that is discretely energy conserving on hybrid unstructured grids, thus allowing numerical simulations at high Reynolds numbers corresponding to operating conditions without using artificial numerical dissipation This paper deals specifically with the simulation of the gas phase flow through realistic gas turbine combustors and the implementation of combustion and spray models that are needed to predict and control the combustion phenomena in these geometries Results from several simulations and comparison with experimental data are used to validate this approach In particular, a complete simulation of the unsteady flow field in a realistic combustor geometry is carried out Some preliminary results for reacting flow simulations in gas turbine combustors are also discussed We discuss several challenges related to large-scale simulations of the flow in realistic combustors, including methods to further accelerate the algorithm’s convergence (eg, use of multigrid techniques), improvement of the parallel performance of the flow solver for two-phase flow simulations (eg, use of dynamic load balancing that accounts for the additional CPU time spent in the spray module when particles are present in the cells)Copyright © 2003 by ASME

Large Eddy Simulation of the NASA High-Lift Common Research Model

Abstract: This brief describes follow-on work to earlier research at the Center for Turbulence Research (Lehmkuhl et al. 2018; Goc et al. 2019, 2020a,b, 2021), where wall-modeled large-eddy simulation (WMLES) was used to simulate a realistic aircraft in landing configuration across the lift curve. This work differs from the previous investigations in that the focus is no longer on the JAXA Standard Model configuration (Ito et al. 2006), but rather on the NASA High-Lift Common Research Model (CRM-HL), which is set to become the new benchmark validation case in the field of computational aerodynamics of high-lift flows (Lacy & Sclafani 2016). In this work, we seek to apply lessons related to modeling choices and gridding approach from three years of experience in the simulation of flows in this regime to accurately predict aircraft maximum lift to within the tolerances (e.g., ∆CL ≤ 0.03 at maximum lift) required by the aerospace industry (Clark et al. 2020).

A dynamic subgrid‐scale eddy viscosity model

Abstract: One major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near‐wall region of a turbulent boundary layer. The results of large‐eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.

Lattice boltzmann method for fluid flows

Abstract: We present an overview of the lattice Boltzmann method (LBM), a parallel and efficient algorithm for simulating single-phase and multiphase fluid flows and for incorporating additional physical complexities. The LBM is especially useful for modeling complicated boundary conditions and multiphase interfaces. Recent extensions of this method are described, including simulations of fluid turbulence, suspension flows, and reaction diffusion systems.

On the identification of a vortex

Abstract: Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor ${\bm {\cal S}}^2 + {\bm \Omega}^2$ are respectively the symmetric and antisymmetric parts of the velocity gradient tensor ${\bm \Delta}{\bm u}$. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier–Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of ${\bm \Delta}{\bm u}$ or the complex eigenvalues of ${\bm \Delta}{\bm u}$, our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.